Initial solar nebula consists of mixtures of grains (rock) and ices.
The initial ratio is about 90% ices and 10% grains

The sun is on so there is a temperature gradient in this mixture:

In the inner part of the solar system, only things which exist
as a solid at high temperature are available (so how come there
is so much water on the earth? -- answer later)

So in the inner part of the solar system you can only make a
rocky planet via acretion of grains.

In the outer part of the solar system, ices can exist so you can
make larger planets out of the more abundant ices

Jupiter (mostly H and He) formed in a manner similar to the Sun,
that is not by accretion. Note that Jupiter can never become
a star. A star is a ball of gas sufficiently hot to excite
nuclear
reactions . The minimum mass require for this is about 8% the
mass of the Sun. Jupiter's mass is an order of magnitude below
this limit. Jupiter will never be a star.

Jupiter has a large mass and perturbs orbits of objects near them.
There were lots of these objects
scattered between Jupiter and Pluto.

Jupiter redirected some of this cometary material into the inner
solar system and most of the earth's water was delivered through
comet bombardment (therefore would we be here without Jupiter?)

Final step is differentiation of the earth: Light objects
float; heavy objects sink.

Iron-Nickel Core (magnetic field) and oxygen-silicon crust

In the outer part of the solar system, the same 4 step process
of accretion occurred but it was accretion of ices (cometisemals)
instead of grains.

Things to note about the formation of planets via accretion

There is a lot of heat dissipated in the final accretion
process resulting in initially molten objects

Any molten object of size greater than about 500 km has sufficient
gravity to cause gravitational separation of light and heavy elements
thus producing a differentiated body

The accretion process is inefficient, there is lots of left
over debris.

In the inner part of the solar system, the leftover rocky debris
cratered the surfaces of the newly formed planets.

In the outer part of the solar system, much of the leftover
rocky debris was ejected from the solar system due to the large
masses of the planets which formed there. Some of this material
was ejected into a large "Comet Cloud" which has a distance of
about 100,000 AU from the Sun and some of the leftover debris (
beyond Pluto) could not be ejected (as it was far away from Uranus
and Neptune) and hence remained there. This material is known as
the Kuiper Belt and it was recently discovered by the Hubble Space Telescope

More information on the Kuiper belt and the kinds of objects that
are located there can be found
here

The asteroid belt represents a relic of the accretion process.
A planet tried to form in that location but the gravitational influence
of the large mass planet Jupiter was sufficient to accelerate the
material there to high velocity. High velocity collisions between
chunks of rocks cause them to be shattered and indeed, over the
history of the solar system, the sizes of the largest asteroids
are decreasing. The asteroid belt is not the remains of a planet
that was blown up by the Death Star.